Category learning is required for guiding everyday perception, action, and decision making. Category learning and the process of categorization is rapid and can be carried out with apparent ease in healthy adults (Homa & Cultice, 1984). One subtype of category learning, prototype-distortion, is intact in populations with severely impaired explicit memory (e.g., amnesiacs: Reber et al., 1998) as well as in patients with impaired implicit memory (e.g., Parkinson's disease: Knowlton et al., 1996). However, recent findings from our laboratory [Little et al., 2004] demonstrate that the neuronal underpinnings for learning related changes in brain activation during prototype-distortion learning implicate a much broader network than previously reported [Aizenstein et al., 2000; Reber et al., 1998]. Further, not only are the learning related changes across a distributed network but the activation within these regions is dependent upon the stage and success of learning [Little & Thulbom, under review]. This leads to a series of questions about the effects of disease and what components of the network are spared to allow intact learning in the presence of other behavioral decrements. Answers to such questions may provide insight into the plasticity of the network that compensate for diseased process. Our long range goal is to define and elucidate the cognitive processes that allow for successful prototype learning in the presence of neurological disease (Keri et al., 2001; Squire & Knowlton, 1995; Knowlton et al., 1996). Knowledge of the redundant processes that allow successful learning in the presence of severe memory deficits may allow better defined and directed programs for remediation and rehabilitation. Our primary objective is to define the role of feedback in successful prototype-distortion learning and conversely those conditions that impair the rate of learning. To do this we will define the role of feedback during prototype-distortion learning while manipulating task difficulty (number of categories, physical similarity between categories) and holding the timing of feedback constant. Secondly, we aim to define the temporal boundaries for the presentation of useful feedback while holding task difficulty constant. Finally, we propose to collect pilot data functional MRI data, on the conditions under which prefrontal cortex is implicated during prototype-distortion learning in response to feedback.